package com.example.HashMapStudy;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

public class HashMapStudy {

    public static void main(String[] args) {
        Map<String, Object> map = new HashMap<>();

        map.put(null, "123");

        map.put("2", null);
        map.put("1", null);
        map.put("5", null);
        map.put("4", null);

//        Map<String, Object> stringObjectMap = Collections.synchronizedMap(map);






    }
}
